How might building a dam on a river that flows to the sea affect a coastal beach? How might building a dam on a river that flows to the sea affect a coastal beach? The cliffs behind the beach experience lower rates of erosion. The beach becomes narrower and the cliffs behind it are subjected to a higher rate of erosion. The cliffs behind the beach have a lower probability of experiencing mass movement. The beach becomes wider, as there is less water input from the river to erode the beach's sand. The coast becomes emergent, as less water is driven to the beach by the river once the river is dammed.

The beach becomes narrower and the cliffs behind it are subjected to a higher rate of erosion.

Explanation:

Building a dam on a river that flows to the sea makes the coastal beach narrow, and the cliffs behind it become subject to a higher rate of erosion.

Due to the damming of inflowing rivers, the sediment supply to the coastal shore becomes limited, making the coast on the opposite side of the dam more vulnerable to coastal erosion. Dams accumulate a significant volume of sand, reducing the amount of sand accessible to beaches, which narrow as a result.

answer at the divergent plate boundary in the middle of the ocean;